FIG. 1 is a block diagram showing a conventional reflection characteristic measuring apparatus with the use of a spectrum analyzer. Upon the receipt of an output signal from a tracking generator 2 of synchronous transmitter type, reflection signal separator 3 allows a reflection signal from a to-be-measured object, e.g.) circuit network 4 to be supplied to spectrum analyzer 1 which is comprised of a 1-channel heterodyne receiver. Reflection signal separator 3 is called an impedance bridge.
As shown in FIG. 1, the output signal of tracking generator 2 is coupled to reflection signal separator 3, and circuit network 4 is connected to a measuring terminal side of reflection signal separator 3 so that a reflection signal from circuit network 4 is separated by separator 3 and supplied to an input terminal of spectrum analyzer 1. In this way, it is possible to measure the reflection characteristic. Here it is to be noted that circuit network 4 terminates in reflectionless terminating device 5.
FIG. 2 is a block diagram for measuring the transmission characteristic of circuit network 4. This measuring circuit is comprised of tracking generator 2 and circuit network 4 to measure the transmission characteristic in circuit network 4.
In the method for measuring the aforementioned transmission/reflection characteristics using the spectrum analyzer as shown in FIGS. 1 and 2, the transmission and reflection characteristics cannot simultaneously be measured due to only one channel being present at the input of the spectrum analyzer. Furthermore, if a measuring signal is switched by a switching device to measure both the transmission and reflection signals, then no exact result of measurement can be obtained due to a variation in the reproducibility of the switching device and in the condition of matching.